Proportional divider



NW, 1949 J. KURMER PROPORTIONAL DIVIDER 2 Sheets-Sheet 1 Filed July 27, 1948 3 ,w W W Z 7 3 W z k. 3 3 F. W

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PROPORTIONAL DIVIDER Filed July 27, 1948 2 Sheets-Sheet 2 WW. w

Patented Nov. 8, 1949 UNITED P'ROPORZI'IONAL DIVIDER' J Jjohna Kurmer, Philadelphia, 2a. Application 1111x227, 1948',fS.eria1'No. 40,869

o '1 'This invention lrelates 'to 'proportional dividers 'and` is parti'cular'ly concerned 'With 'the prov'ision of' an 'instrument of this kind in 'which is possible `to lset the 'points at one end of 'the 'instrument 'to' a desired' 'intervaf 'and' 'then to lock' 'and hold 'them' 'in fixed yrelationsl'ii'p while 'setting' the points 'at' the opposite 'end to 'some other interval 'by' adj usting' the 'position of the' upon which 'the 'two 'legs of the 'dividers are adapted' to swing. After this has been done it is' also 'an object of myinvention to provide 'means 'whereby the leg pivot 'may be' locked' in the vposition which 'it' assum'ed in establishing: the interval between said second pair ofpoi'nts so' that said first lock'may be released and the 'instrument used' 'asl a pro'- portional dividers. At' 'the same time` it is an object of' the invention to provide an instrument of the' character` described which is simple, rugged', accurate, easily manipulated and relatively inexpensive to manufacture.

How 'the foregoing' objects are atta'ined'is illustratecl in preferred form. in the 'accompanyng drawings wherein':`

Figure' 1 Vis a pl'an view of my improved 'instrument with 'the' divider vlegs in partly'opened position;

Figure 2 is a section 'onfan enlarg'edscale taken as indicated' by the line 2--2- on Figure '1;

Figure 3 isv a section, also on .an enlarged scale,

taken as indi'cated by the line 3-3' on Figure '1;

Fgure 4 is a section on line 4-ll` of'Ei'gure. 2`;

Figure '5 is a top end view of Figure 1;,

Figure 6 is a side view of Figure 1;,

Figure "7 is an end'vi'ew showing'how the points of the diviers legs are 'bent in sothat. they coincide when the 'legs of' the instrument are in closed position; and` Figure 8' "is a section takenV asindicated by the line 8-8 ofFi'gure Z'but' with the legs of the instrumentl in closed position in order to better illustrate certain. of' the features of m'y i'nvention.

The divider legs 9 and HI' of my improved instrument are, provided with divider pi'ns I'l', l2, l'`3= and` l`4* which are arranged at right angles to the p'lane in which the legs swing around the pivot shaft I'5. The bodiesw of these .pins are held in. their perpendicular trelationship to the legs by means of bushings a, |2a, l'3a andA Ma and are adjustable asv to depth andv held in place by the set screws ilb, 12h, [3b and Mb.

At their lower ends' the'- pins are bent 'inwa-rd 'so that their tips or points 'willlie along theucenter'line of the legs' 9 and l' 'and ifurtherso that the'twotipsfiat each emoi the divider maycoino 2? side-'when the'legs are in closed' position' 'a's shown in Figura '7.

A third, or *what I' 'term a mreferenceleg* W, is inserted' between' the divider'l'eg's '9 andl'f, one end of which' reference 'leg 'is provided with 'a slotted guideway vv|f'l'a1`ong one'side'of' which'vis'a rack 18'. The yg'uideway'is'mill'ed out or'machine'd above andf below to provide a ``central1 shoultl'ered porti'on |59' at each side of the' sl'ot. The opposite 'endV of the' reference leg'is rediu'ced* thi'ckfness in order 'to Vprovide room' for' the 'accormnodation of' the looking arms 20 and A'ZI' which' will be describedf more fully 'later on inconnection With the looking assembly.

' `The en'ds of the-dividerlegsin 'which the `pifvot shaft is located are v'also provided? with 'sl'otted guideways 22 and 23, the 'inner' faces oftheflegs being machined' or milied out to provide the shouldered; port'ionsfl 24 and '25.

The pivot sh'ai't'- "I'5 is' part of what' Ii term 'a pivot assembl'y', and lassein'ioly' inciudes addition 'an upper 'slide I262, -a 'lower' slide- !flf, an upper intermediate' slide '2533 andv 1a lower' intermediate slide 2/91, ftlie slid'es 'a'n'd'i lhewing central proje'ctions '26a' and 21a' i'ntoftlic slots ``2'2 and 23, theslides' '28 and? 219 adapted'- to move along' the silfmdldered portioi-rs 24 and '25- respectively. Therefare also inciued in the assem'bl'y ian upper slide1 w afilower slide l31| which are adapted 'to `mow-e along the centralshoulder or shel'i` If-H of the 'reference leg -|6. 'Between the slid'es 282 'an'df 30, anothetween the vslid'es 2-'9' and 3.|` are .suitable 'spacer washers- 332' and' 33', these 'washers` being' 'of =a thickness' which `willi insure the existence of 'a snug` but. sliding' -fitbetween 'the'fconti'guous faces of the legs 9; llTJ-and 116. 'Thisffprevents coclifng' of' the 'legs respect :to zone: another and sures movement' thereo'f truly parallel'EV planes.

Centrally the shaft 15 is formed with an integral pinion 3'4 which 'is adaptediftofimesh'with the teeth onftherack |I8', 'andf on'itsfupp'erxsquared portfon lla'- i'sfitte'df :a thumb wheel! 'by 'means of which the shaft mayfibe rotated. A collar ror nut 3'5 at the too and another' 3W at'- the' bottom of` thel shaft |=5fl serve to hold' the. assei-nlbly' together, these nutsl or co'l'lars pref'erabiy' being? pinned' to the shalft by the pinstaand-311m, or otherwise suitably' fixed to'4 the' shait. -It should be noted that the thi'cikness ordbpthoi the fpini'on 34 should be 'exactly 'the' same vas 'the 'thicltness of the Shoulders P9' onwhich thesllides it-aml- 3| are adapted to rest. I-n-thisway; 'when the pivot assembly` 'is locked into position, as: w'illl be' scribed below, the 'reference 'legfbec'o'me's with relation to the pinion because the shoulders and the pinion will be gripped by the slides.

At the underside of the instrument I provide the looking or clamping plate 38 having an enlarged central aperture 39 which fits around the lower end of the shaft |5. This plate is roughly coextensive in length with the length of the adjacent slide 21 as shown to best advantage in Figure 8, and at one end of the plate 38 is a set screw 40 the point of which is adapted to project into a hollow 4| in the adjacent face of the slide 21. At the other end the plate carries a thumb screw 42 the point of which is adapted to fit into a hollow 43 in the adjacent face of the other end of the slide 21. It will be obvious that by means of this clamping plate with its set screw 40 and thumb screw 42, it is possible to clamp together all of the parts which are mounted upon the pivot shaft |5.

To go back to the looking assembly, which includes the arms 20 and 2|, it should be pointed out first that these arms are of equal length and that their inner ends are coupled together at the center upon a pivot in the form of a thumb screw 44, the end of each being provided with an enlarged hub portion 45 for this purpose. These hub portions have central sleeve portions 46 around which is located a slide 41 adapted to move along the slotted longitudinal guideway 43, which latter constitutes a second guideway in the leg |6 formed in the end opposite to the guideway and the rack |8. The screw has a shoulder 44a which abuts against the upper hub 45 and the central reduced portion 44b is free to rotate in the upper hub 45 but is threaded into the lower hub 45 as shown to best advantage in Figure 3. It will be seen, therefore, that when the screw is turned down the two hubs 45 are drawn together in order to clamp them tightly against the opposing faces of the leg |6. The opposite end of the arm 20 is pivoted at the adjaoent outer end of the leg 9 upon a pin 20a the axis of which coincides with the point of the corresponding divider pin. Similarly, the outer end of the arm 2| is pivoted upon a pin 2 |a the axis of which ooincides with the point of the corresponding divider pin |2 on the adjacent end of the divider leg Ill.

The inner corners of each end of both of the divider legs are slotted as at 49, which slots are adapted to embrace the adjacent divider pins so that the instrument may be fully closed and the points of the pins brought together as shown in Figure '7. Also, the upper arm 9 is slotted as at 50 to accommodate the shank of the thumb screw 44 and the inner face of the leg is recessed as at to accommodate the hub 45 of the arm 2|. The inner faces of the lower ends of the divider legs 9 and |0 are each equipped with a stop lug or pin 52, the axis of which is located on the center line of the leg and against which the lower end of the reference leg |6 is adapted to abut. The legs may be provided with whatever scales are desired, in the present instance the upper leg being shown as having a scale 53 which cooperates with an index point 54 on the upper slide 26.

The procedure to be followed in using the instrument will now be described.

1. With the screws 42 and 44 retracted or in their loosened position, close the legs completely.

2. Now, shift the reference leg |6 until its lower end touches the stop pins 52.

3. Tighten the thumb screw 44 and then move the pivot as close to a 1:1 ratio as possible by rotating the shaft |5 by means of the thumb wheel 35 which, of course, will turn the pinion 34 and cause the entire fulcrum assembly to slide along the guideways in the legs.

4. Now, tighten the thumb screw 42 in order to clamp the parts together around the shaft I 5 and loosen the thumb screw 44.

5. The points of the divider pins and |2 should now be set to span the larger of the two desired intervals, after which the thumb screw 44 should be tightened and the thumb screw 42 loosened.

6. The thumb wheel 35 is then turned in order to slide the pivot assembly to the position it must occupy where the points of the pins |3 and |4 span the second and smaller of the two desired intervals.

7. When this has been accomplished, tighten the thumb screw 42 and loosen the thumb screw 44 and proceed to use the instrument as a proportional dividers.

It will be seen that the leg |6, which I term a "reference leg, is in reality a "floating member in my instrument. It is made shorter than the divider legs 9 and IE) so that when the divider is closed and all the legs coincide, the leg |6 can be shifted slightly from one end to the other until stopped either by the pins 20a and 2|a at the top or by the stop pins 52 at the bottom. This floating feature compensates for the shift-ing of legs 9 and |0 with respect to leg IB which occurs. when the position of the pivot assembly is changed while the looking arms 20 and 2| are rigidly fixed. If the leg IG were not shorter than the legs 9 and |0, and a change in the pivot position were made under the conditions described above, then it would not be possible to close the dividers due to the shifting mentioned.

It will be understood, of course, that the operator initially positions the leg Hi as favorably as possible considering the ratio to be employed. For example, if while the divider is closed, the pivot assembly initially is Vin approximately the 1:1 position, then the leg lt should be placed against the stop pins 52, but should the fulcrum initially be in the 10:1 position, then the leg |6 is moved against the pins 20a and zla.

In using the instrument, the end of the dividers which can be locked by the arms 26] and 2| and the thumb screw 44 is always set first and to the larger of the two desired intervals, after which the other end of the dividers is set to the smaller interval in the manner described.

It will be seen that if the proper lock-unlook sequence is used with the thumb screw 42 and 44 then the looking arms 20 and 2 since they are of equal length, will insure that the legs 9 and |0 form equal angles with the leg |6 which in turn assures the formation of two similar triangles, namely, one triangle whose apices are at the pivot center, the pin 20a center and the pin 2 la center, and a second triangle whose apices are at the pivot center and at the Centers of the pins 52. Hence proportionality exists between the bases of these two triangles.

I claim:

1. Proportional dividers comprising a pair of divider legs, a, pivot assembly connectinf,r said legs and adjustable longitudinally thereof, divider pins arranged at right angles to the plane in which the legs swing around the pivot, a reference leg having a longitudinal guideway along which said pivot assembly is adapted to travel, a looking assembly consisting of a pair of arms of equal length pivoted together at one end with the opposite end of one arm pivoted to the end of one of the divider legs on an axis coinciding With the point of the corresponding divider pin and with the opposite end of the other arm similarly pivoted to the cooperating end of the other divider leg, said reference leg vbeing provided with a second longitudinal guideway along which the pivot of the looking assembly is adapted to travel, clamping means for holding the pivot assembly in a selected position, and clamping means for looking the pivot of the looking assembly in a fixed position with relation to said second guideway in the reference leg.

2. The dividers of claim 1 in which the pivot assembly for the divider legs includes a rotatable pivot shaft having a pinion and in which said first guide in the reference leg is provided with a rack arranged to mesh With said pinion.

3. Proportional dividers comprising a pair of divider legs, a pivot assembly, guideways on the legs, said pivot assembly including slides adapted to move along said guideways, divider pins arranged at right angles to the plane in which the legs swing around the pivot, a reference leg having a, longitudinal guideway at one end with a rack therealong, said pivot assembly also including slides adapted to move alongsaid guideway in the reference leg, a looking assembly consistlng of a pair of arms of equal length pivoted together at one end with the opposite end of one arm pivoted to the end of one of the divider legs on an axis coinciding with the point of the corresponding divider pin and With the opposite end of the other arm similarly pivoted to the cooperating end of the other divider leg, said reference leg being provided at its other end with a second longitudinal guideway, a slide associated With the pivot of the looking assembly and adapted to move along said second guideway, a rotatable pivot shaft associated with the pivot assembly for the divider legs including a pinion meshing with said rack, a thumb wheel for rotating said pivot shaft and its pinion, means for clamping the pivot assembly slides against the sides of the several legs, and clamping means for locking the arms and the pivot of the looking assembly in a fixed position with relation to said second guideway in the reference leg.

JOHN KURMER.

No references cited. 

